(218b) Sustainability and Economic Evaluation of Tannery Wastewater Treatment Pathways Using the P-Graph Approach

Authors: 
Aboagye, E. - Presenter, Rowan University
Desai, M., Rowan University
Pimentel, J., Grupo de Procesos Quimicos y Bioquimicos, Universidad Nacional de Colombia, Bogota, Colombia
Tran, C., PSEG Institute for Sustainability Studies
Orosz, A., University of Pannonia
Cabezas, H., University of Miskolc
Friedler, F., Department of Computer Science, University of Veszprém
Yenkie, K., Rowan University
The growth in world population has increased the pressure on freshwater demand. One of the mitigation approaches to meet this growing demand is wastewater treatment (Alasino et al., 2007; Crini and Lichtfouse, 2019; Inc et al., 2002). However, the treatment of wastewater for reuse must be given a holistic view by incorporating the techno-economic analysis and sustainability assessment simultaneously (Yenkie, 2019). The often-conflicting views of economics and sustainability associated with industrial processes can be bridged through the application of optimization methods.

The tannery industry is a major source of wastewater. It is important to treat it carefully due to the presence of high levels of contaminants, especially chromium. Treated tannery wastewater is beneficial for irrigation purposes due to the presence of nitrogen, phosphorus, potassium, and organic matter (Saxena and Bharagava, 2016). The stagewise treatment of wastewater presents a viable way of capturing all the complexities associated with the process.

The objective of this work is to provide multiple feasible pathways to tannery wastewater treatment by quantifying simultaneously the economics and sustainability. This is achieved by developing an Excel-based P-graph tool that gives the n-best feasible pathways ranked from least to highest based on cost and sustainability metrics.

In this work, treatment technologies were categorized into stages based on their efficiencies, driving forces for contaminant removal, and composition of wastewater. Further, due to the difference in efficiencies of technologies within a stage, treatment options of higher efficiency were preceded by options with lower efficiency. Through this approach, a maximal treatment structure was generated. Economic models were incorporated consisting of investment and operating costs. The sustainable process index (SPI), which has been used extensively to assess the ecological footprint of industrial processes was used as the sustainability metric (Krotscheck and Narodoslawsky, 1996; Narodoslawsky, 2015; Narodoslawsky and Krotscheck, 2004). The SPI methodology was used to evaluate the total area needed to provide a unit (1m3) amount of treated wastewater. There are seven footprints associated with the SPI methodology which can be categorized into two broad areas, namely input and output. Input areas account for the resources that are consumed by the process while the output indicates that needed to embed products and emissions into the ecosphere. The P-graph approach, a graph-theoretic framework for the synthesis and optimization of process networks, was implemented by developing an Excel-based realization of software (Cabezas et al., 2018; Friedler et al., 1993; Heckl et al., 2010; Yenkie et al., 2021). The optimization problem was solved formulating a mixed-integer linear programming problem and employing the accelerated Branch-n-bound algorithm in the Excel-based P-graph tool. Figure 1 summarizes our scope of work for the tannery wastewater case study.

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